The Tweet: “More than 80% of the Earth’s natural forests have been destroyed.”

Forests cover 31 per cent of the world’s total land area, according to a report published by the World Resources Institute (WRI) in 2010. This is approximately 4 billion hectares. Deforestation is mainly a response to the demand for agricultural land. Tropical forests are being cut down to make way for crops, although deforestation is slowing. In the last decade 13 million hectares of forest were converted into agricultural land compared to 16 million in the previous decade.

However, the net loss of forest is slowing significantly, as trees are replaced as part of sustainability programmes. The net change in forest area between 2000-2010 is estimated at -5.2 million hectares per year, down from -8.3 million per year between 1990-2000.

So while deforestation is still an issue, and forested land continues to decrease significantly each year, sustainability programmes like the United Nations REDD scheme are having an effect.

The report by the WRI is also the source to the claim that 80 per cent of the world’s natural forests have been lost to deforestation, according to news reports like this one from October 2014. However, reading the report there is no mention of this statistic, nor is there any mention on the WRI website and it seems extraordinary that such a figure would be accurate. Firstly, the report, as stated above, puts the current forest cover at 4 billion hectares. Estimates of the Earth’s total land surface vary between 13 and 15 billion hectares. This means that if we have lost 80 per cent of our forests the original forest cover would have been greater than the total surface area of the Earth, assuming only a small amount of reforestation has taken place.

The United Nations Food and Agriculture Organization estimates that the pre-industrial forest cover was 5.9 billion hectares, 1.9 billion more than the current level. Since humans have developed machinery we have lost approximately 30 per cent of the world’s natural forests. Although the levels of deforestation are less alarming than this tweet suggests the net loss of forest is still high and sustainability programmes are only beginning to have an effect.